1. Field of the Invention
The present invention relates to a read only memory (ROM) data verification circuit for checking whether or not data have correctly been written into a ROM device (or a ROM) or into a plurality of ROM devices (or a plurality of ROMs).
2. Description of the Prior Art
FIG. 9 is a block diagram showing a configuration of a conventional ROM data verification circuit. In FIG. 9, the reference number 91 designates a Read Only Memory (ROM) for storing programs and data items, the reference number 94 denotes output ports through which addresses from a Central Processing Unit (CPU) and data items from the ROM 91 are output externally, and the reference number 93 indicates the CPU for controlling the operation of the ROM 91 and the output ports 4.
Next, a description will be given of the operation of the conventional ROM data verification circuit.
FIG. 10 is a flow chart showing the operation of the conventional ROM data verification circuit shown in FIG. 9.
In order to check whether data such as programs, control data, and other types of data have correctly been written into the ROM 91, the conventional ROM data verification circuit performs the following test.
First, the CPU 93 in the conventional ROM data verification circuit executes an instruction "MOV" as one of instructions described in a test program, so that data written and stored in the ROM 91 are read out per byte. Then, the data that have been read out are output to external devices (not shown) through the output ports 94 (Step ST102). Next, the data read out are compared with expected data that have been prepared in advance (Step ST103). Based on the comparison result obtained by the step ST103, it is possible to verify whether the data have correctly been written into the ROM 91. The completion of the comparison operation for all of data items stored in the ROM 91 (Step ST104) leads the completion of the test operation.
Since the conventional ROM data verification circuit has the configuration described above, the data size that are read out from the ROM 91 at once is small, so that it takes a long time period to perform the test operation for the data stored in the ROM 91. Recently, the memory size (or the volume) of ROM devices is increasing and the amount of data to be stored in the ROM devices is also increasing. This causes to increase the time period of the test operation to be required for checking whether or not data have correctly been stored into ROM devices. In addition, the size of test programs and test vectors to be used for testing data stored in the ROM devices are increased. This also causes to increase the time period of the test operation.